Many attempts at providing reliable hazard target discrimination have been carried out in the field of vehicular radar systems which provide target range and relative velocity measurements thereof. The operating environment of an automotive radar system presents many challenges to the system designer, among the most troublesome being differentiation between hazard and non-hazard targets, both of which return transmitted radar signals. Typical non-hazard targets include road signs, bridges, fences, guard rails and road-side burms, etc. Poor discrimination of such non-hazards from hazards of course limits the effectiveness and reliability of automotive radar systems.
Various attempts in the art have been made to remedy these radar system shortfalls. One such example of these attempts includes limiting the range and pattern width of signal transmission and reception which, in turn, also undesirably limits the area of detection. This is an especially unattractive option where, as in a vehicle blind-zone detection radar system, a relatively wide area needs to be covered. Other proposals for solving these radar system short-falls includes multiple transmitter and/or receiver configurations which, of course, add complexity and cost.
Variable transmitted radar pattern angle and range, interactive in response to steering input, have also been proposed to limit return signals from non-hazard targets such as chose which are tangential to a vehicle's travel around a curve or bend. This technique may be useful for look-ahead or look-back radar systems where radar pattern is substantially aligned with the major axis of the vehicle but does not address the problems of blind-zone radar systems where the transmission pattern is intentionally at an angle from the major axis of the vehicle.
In addition, radar system have been proposed which use relatively complicated methods such as return signal processing to separate multipath signals in frequency bands or which consider a combination of range and a target's radial velocity with respect to the vehicle.
A further prior art system uses a side mirror mounted look-back radar system to determine the relative velocity of a target in an adjacent lane. This system requires a narrow beamwidth of .apprxeq.5.degree. for proper coverage, which is difficult to achieve at low cost.